The overall aim of this large multicentre community based study of young men and women is to examine the occupations, industries and exposures in the work-place which are associated with a high risk for asthma and other adverse respiratory health effects, with particular emphasis on specific exposures of predominantly female occupations (irritants, detergents and other asthmagens), and of other high risk major occupations which have not been adequately examined. The main hypotheses of the study are that respiratory diseases are strongly related with exposure in the workplace, that a considerable proportion of adult onset asthma is associated with these exposures and that the importance of occupational risk factors for asthma has been underestimated, particularly among women. The occupational asthma study (ECRHS- OA) forms part of a wider international multicentre survey on respiratory health (European Community Respiratory Health Survey- ECRHS). The first phase of the ECRHS was conducted in 1991/92 and examined risk factors for asthma and atopy in subjects aged 20-44 years. The study is currently updated (ECRHS-II) following-up approximately 17,000 young adults from 12 countries (Australia, Belgium, France, Germany, Iceland, Italy, Norway, Spain, Sweden, Switzerland, UK and USA). Those subjects who took part in the first survey will be re-contacted in 1999, to determine risk factors for incidence and remission of asthma, other respiratory symptoms, atopy, changes in bronchial responsiveness and lung function. Subjects will be asked to perform a forced spirometry, methacholine challenge and to provide blood samples for IgE testing. A questionnaire administrated by trained interviewers will be delivered requesting information on respiratory symptoms and diseases, socio-demographic factors, tobacco smoking, complete occupational history since the last survey, environmental exposures, family history, diet, treatment and use of health services. Modular occupational questionnaires will be developed for subjects employed as cleaners, homemakers, welders, metal workers, nurses, and subjects exposed to organic dusts in the paper and textile industries. The study will provide valid and precise estimates on the importance of specific occupations, industries and exposures in relation to asthma incidence and prevalence, similar estimates for other respiratory symptoms and diseases and also for declines in pulmonary function.